As a result of the progress in molecular biology, in cell biology and in genetics, many tools are now available for modifying a cell, whether it is a prokaryotic cell or a eukaryotic cell such as yeast.
For example, it is possible to obtain a cell which produces or uses new compounds, or else to improve the properties of a cell, by using gene modification techniques, whether by integration, deletion or disruption of DNA sequences, or by site-directed or random mutagenesis.
Those skilled in the art also have available older techniques such as crossing techniques.
Those skilled in the art can also combine these techniques, for instance carrying out a mutagenesis on a genetically modified strain of yeast, or genetically modifying a strain of yeast obtained by crossing.
However, those skilled in the art are sometimes limited by the laboriousness, the time required and the lack of efficiency of the known techniques for obtaining the desired improved cell.
The modification of a yeast strain makes it possible to obtain yeasts with different or improved properties, which can be used in many possible applications, among which breadmaking, the food industry, health, the production of compounds, for example alcohol, the production of yeast extracts.
The crossing of yeast strains is a technique which is widely used, but which often requires optimizations in order to increase the chances of obtaining the desired yeast strain, for example the selection of segregants on the basis of particular properties.
However, the lack of efficiency of the crossing of yeast strains is far from being solved for all situations. For example, it is difficult to envision using the crossing technique starting from a yeast strain which has undergone several genetic modifications. This is because the probability of obtaining segregants having all the genetic modifications of the starting strain decreases with the number of genetic modifications.
Thus, there is still a need to provide novel methods for obtaining improved strains of yeast, these methods being faster and simple to carry out and allowing a more efficient selection of the yeast strains having the desired improvements.